Promotion of liver growth by CAR is accompanied by Akt pathway activation and FoxM1-Nedd4-mediated repression of PTEN

Promotion of NR1I3-mediated liver growth is accompanied by STAT3 activation

BACKGROUND

The constitutive androstane receptor (CAR, NR1I3)-mediated mechanisms regulating hepatocyte proliferation and growth of the liver did not yet experience complete elucidation. We investigated whether STAT3 could be activated in vivo by NR1I3 signaling in mouse liver.

METHODS AND RESULTS

Using Western blot analysis, immunofluorescence assays and real-time PCR we established the state of STAT3 activation when it comes to the mouse liver subsequent to treatment ofNR1I3 agonist,1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP). STAT3 nuclear relocation and hepatocyte growth were both induced by NR1I3-mediated phosphorylation of STAT3. Moreover, the NR1I3-STAT3 signaling pathway's proliferation impact was facilitated, partly, by cMyc and Cyclin D1 upregulation.

CONCLUSIONS

This work's evidence demonstrates that NR1I3-pushed STAT3 activation contributes to TCPOBOP-induced liver growth and hepatocyte proliferation, at least in part, through its molecular targets cMyc and CyclinD1.

Noncanonical Constitutive Androstane Receptor Signaling in Gene Regulation

The constitutive androstane receptor (CAR, NR1I3) is extremely important for the regulation of many physiological processes, especially xenobiotic (drug) metabolism and transporters. CAR differs from steroid hormone receptors in that it can be activated using structurally unrelated chemicals, both through direct ligand-binding and ligand-independent (indirect) mechanisms. By binding to specific responsive elements on DNA, CAR increases the expression of its target genes encoding drug-metabolizing enzymes and transporters. Therefore, CAR is mainly characterized as a ligand-dependent or ligand-independent transcription factor, and the induction of gene expression is considered the canonical mode of CAR action. Consistent with its central role in xenobiotic metabolism, CAR signaling includes a collection of mechanisms that are employed alongside the core transcriptional machinery of the receptor. These so-called noncanonical CAR pathways allow the receptor to coordinate the regulation of many aspects of cell biology. In this mini-review, we review noncanonical CAR signaling, paying special attention to the role of CAR in energy homeostasis and cell proliferation.